Wideband code division multiple access (WDCDMA) networks transmit information in frames. Each frame includes multiple slots and each slot includes multiple chips. Each slot starts by a primary synchronization code (PSC) and a secondary synchronization code (SSC). The PSC is the same for each slot of the frame while the SSC is used to encode a code group number and can differ from one slot to another. A frame can include fifteen slots, each slot can include 2560 chips and each of the PSC and SSC can include 256 chips.
In WCDMA mobile devices, cell search (search for available base stations) can be performed in three scenarios: initial cell search that occurs when a mobile device is switched on, idle mode search that occurs when the mobile device is inactive, and active mode search during a call.
The cell search is characterized by a high computational load and multiple memory accesses. It requires a dedicated slot synchronizer and a dedicated frame synchronizer, each consuming a substantial amount of power and spanning over a substantial integrated circuit real estate.
A Slot synchronizer includes a dedicated matched filter that is applied to the input data to detect slot boundaries. The filter impulse response matches the primary synchronization code (PSC). After accumulation among several slots (groups of chips) and sorting, a number of candidates are identified as possible slot boundary candidates.
A frame synchronizer includes a correlating circuit that evaluates all possible SSCs by correlating them with input data that represents the received SSCs for all found slot boundaries. The correlation results are used for decoding the SSC group number.